Porous metallic material having high specific surface area, method of producing the same, porous metallic plate material and electrode for alkaline secondary battery

ABSTRACT

The porous metallic material of the present invention has an overall porosity of 80 to 99%, and a skeleton in a three dimensional network structure which is entirely composed of a sintered metal powder having a porosity of 10 to 60%. The specific surface area is very high, for example, 300 to 11000 cm 2  /cm 3 . The porous metallic material can be reinforced by a reinforcing plate. The porous metallic material is also suitable for an electrode of an alkaline secondary battery and enables achievement of increases in the life and the amount of the active material contained therein. The porous metallic material can be produced by preparing a foamable slurry containing a metal powder, forming the foamable slurry, drying the formed product, preferably after foaming, and finally burning the dry formed product.

TECHNICAL FIELD

The present invention relates to a porous metallic material having a high specific surface area, a method of producing the same, a porous metallic plate material and an electrode for an alkaline secondary battery such as a nickel-cadmium battery, nickel-hydrogen battery or the like.

BACKGROUND ART

Porous metallic materials having a three-dimensional network skeleton in which pores are formed are conventionally used as structural members of various machines and apparatus. For example, such metallic materials are used as an active substance holding material of an electrode of an alkaline secondary battery, a hydrolytic electrode, a kerosene atomizing member of a petroleum heater, a magnetic shield packing, a gas expansion buffer of an air cushion using an explosive, a sound absorbing material, various filters such as a hydrolytic filter of a clarifier, an electrostatic filter of an air clarifier, an oil mist filter for an engine exhaust gas, a filter of a high-temperature exhaust dust collector, etc.

An example of known porous metallic materials is a material having a skeleton which is obtained by plating a spongelike resin and then burning the resin, and which has pores formed therein by burning, as disclosed in, for example, Japanese Patent Laid-Open Patent Application No. 5-6763. This porous metallic material has a specific surface area of 5 to 75 cm² /cm³ and a porosity of 92 to 97%.

However, it has been required to increase the porosity and specific surface area of the porous metallic material with recent increases in the performance and output of various machines and apparatus and recent decreases in the weight thereof.

On the other hand, an electrode for an alkaline secondary battery such as a nickel-cadmium battery, a nickel-hydrogen battery or the like is produced by a method in which a spongelike porous metallic substrate having pores formed by three-dimensional continuous network connection of a skeleton consisting of a Ni metal is impregnated with a paste formed by kneading an active material powder with a viscous aqueous solution containing 1 to 2% of CMC (carboxymethyl cellulose) and PTFE (polytetrafluoroethylene), dried and then rolled.

The spongelike porous metallic substrate comprising the pores and the skeleton and used for producing an electrode for an alkaline secondary battery can be obtained by Ni-plating an urethane foam, and then burning the urethane foam. The spongelike porous metallic substrate obtained by burning the urethane foam has the skeleton having the pores formed by burning the urethane, and generally has an average pore size of 400 to 600 μm, a porosity of 93 to 97% and a specific surface area of 40 cm² /cm³.

For a nickel-cadmium battery of alkaline secondary batteries, nickel hydroxide powder and cadmium hydroxide powder are used as a positive electrode active material and a negative electrode active material, respectively. On the other hand, for a nickel-hydrogen battery, nickel hydroxide powder and hydrogen occluding alloy powder are used as a positive electrode active material and a negative electrode active material, respectively.

When a closed alkaline secondary battery containing a conventional electrode in which pores of a spongelike porous metallic substrate are filled with an active material is repeatedly charged and discharged, the characteristics thereof gradually deteriorate, and the service life is limited to 500 to 1000 times of charging and discharging operations. The deterioration in the closed alkaline secondary battery is caused by an increase in internal pressure due to exhaustion of an electrolyte in a separator. It is said that the exhaustion of the electrolyte is caused by solidification of the electrolyte due to corrosion of the alloy, a change in electrolyte distribution due to swelling of the positive electrode, etc.

Corrosion of the alloy includes corrosion of a metallic member such as a battery can and corrosion of the hydrogen occluding alloy of a nickel-hydrogen battery, and represents the phenomenon that a part of the electrolyte is solidified to produce a corrosion product due to corrosion, thereby decreasing the amount of the electrolyte.

Swelling of the positive electrode is caused by the phenomenon that, when nickel hydroxide as the positive electrode active material is changed to --NiOOH through a crystal structure --NiOOH and --Ni(OH)₂ by repetition of the charging and discharging operations, respectively, micropores referred to as "mesopores" are formed in the particle surfaces of the positive electrode active material powder, the electrolyte permeates into the mesopores due to the capillary phenomenon, and thus unevenly distributed in the positive electrode, thereby decreasing the amount of the electrolyte in the separator.

Since the conventional alkaline secondary battery does not have a sufficient life, as described above, an alkaline secondary battery having a longer life is demanded.

It is also known that the capacity of the closed alkaline secondary battery containing an electrode increases as the amount of the active material contained in the electrode increases. However, in an electrode comprising the spongelike porous metallic substrate having pores which are formed by three-dimensional continuous connection of the conventional skeleton consisting of a Ni metal, since the pores formed in the skeleton by burning are closed and filled with no active material, the amount of the active material contained in the electrode is limited. There is thus demand for an electrode containing an increased amount of active material.

DISCLOSURE OF THE INVENTION

In research for developing a porous metallic material having a higher specific surface area than that of the conventional porous metallic material from the above-mentioned viewpoints, the inventors obtained the following results:

A foamable slurry having a composition comprising the following components as raw materials, for example, % by weight ("%" indicates "% by weight" hereinafter) is prepared:

0.05 to 10% of water insoluble hydrocarbon organic solvent having 5 to 8 carbon atoms;

0.05 to 5% of surfactant;

0.5 to 20% of water soluble resin binder;

5 to 80% of metal powder having an average particle size of 0.5 to 500 μm, and, if required;

0.1 to 15% of plasticizer comprising at least one of polyhydric alcohols, fats and oils, ethers and esters; and

the balance consisting of water.

The foamable slurry is formed into a predetermined shape by a known method such as a doctor blade method or a slip cast method, and then maintained at a temperature of 5° C. or higher, to form a porous product having many regular fine cells. The fine cells are generated by vaporization of the water insoluble hydrocarbon organic solvent from the formed product because the solvent has a higher vapor pressure than water. The porous formed product has strength which allows handling due to the water soluble resin binder, and plasticity provided by the plasticizer. When the porous formed product in this state is sintered, the metal powder is sintered to obtain a porous metallic material having a skeleton which comprises a sintered metal powder and which has a foamed three-dimensional network structure, as shown in a schematic drawing of FIG. 1.

Unlike the conventional porous metallic material, the resultant porous metallic material has the porous skeleton in which no pore is formed by burning and which comprises the sintered metal powder having a high porosity of 10 to 60%. Although the overall porosity is 80 to 99%, the porous metallic material has a high specific surface area, e.g., 300 to 11000 cm² /cm³.

The present invention has been achieved on the basis of the above-mentioned research results, and is characterized by the porous metallic material having a high specific surface area, an overall porosity of 80 to 99% and the three-dimensional network skeleton structure which is composed entirely of the sintered metal powder having a porosity of 10 to 60%.

The method of producing the porous metallic material of the present invention comprises the slurry preparing step of preparing a foamable slurry containing a metal powder, the forming step of forming the foamable slurry, the drying step of drying the formed product, and the sintering step of sintering the dry formed product.

When forming the foamable slurry into the porous formed product, for example, a reinforcing plate such as a wire cloth is extruded together with the foamable slurry to obtain a porous metallic plate material reinforced by the reinforcing plate. The resultant porous metallic plate material has excellent strength and a high specific surface area.

In addition, as a result of research for further increasing the life of an alkaline secondary battery repeatedly charged and discharged, as compared with conventional secondary batteries, the inventors found that the use of the above-mentioned porous metallic material for an electrode of a secondary battery can increase the life of the secondary battery.

Namely, as shown in FIG. 6, a skeleton 2 of a spongelike porous metallic substrate comprising pores 1 and the skeleton 2 comprises a microporous sintered metal having micropores 11 which are smaller than the pores 1. The skeleton 2 comprising the microporous sintered metal is provided with the electrolyte holding ability so that the electrolyte consumed when the specific surface area is increased due to the formation of mesopores in the powder surfaces of the positive electrode active material is replaced by the electrolyte previously held, by means of capillary force, in the micropores 11 of the skeleton 2 of the spongelike porous metallic substrate, which comprises the microporous sintered metal. When the electrolyte is consumed, the electrolyte appropriately oozes out of the micropores 11 of the skeleton 2, thereby preventing exhaustion of the electrolyte in the separator.

On the other hand, since an electrode is produced by filling both the pores 1 and micropores 11 of the spongelike porous metallic substrate with the active material, the electrode containing a large amount of active material which is uniformly dispersed, as compared with a conventional electrode, can be obtained. The use of this electrode enables production of an alkaline secondary battery having a higher capacity than a conventional secondary battery.

The present invention has been achieved on the basis of the above finding.

The present invention is characterized by an electrode of a secondary battery comprising a spongelike porous metallic substrate comprising a three-dimensional network skeleton and pores which are formed by the skeleton and which are filled with an active material, wherein the skeleton has micropores having an average micropore size of 0.5 to 20 μm and the inside thereof entirely comprises a sintered metal powder having a porosity of 10 to 60%.

If the average micropore size of the skeleton of the spongelike porous metallic substrate which constitutes the electrode of the secondary battery is less than 0.5 μm, capillary force excessively increases, and thus the electrolyte holding ability excessively increases, thereby reducing oozing of the electrolyte. On the other hand, if the average micropore size exceeds 20 μm, the electrolyte holding ability is insufficient, and the strength of the spongelike porous metallic substrate is also insufficient. If the microporous sintered metal of the skeleton has a porosity of less than 10%, the amount of the electrolyte held thereby is insufficient. On the other hand, if the porosity exceeds 60%, the spongelike porous metallic substrate has insufficient strength.

Therefore, in the electrode of the alkaline secondary battery of the present invention, the skeleton of the spongelike porous metallic substrate, which comprises the microporous sintered metal, has an average micropore size of 0.5 to 20 μm (more preferably 1 to 5 μm), and a porosity of 10 to 60% (more preferably 15 to 35%).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in detail below with reference to the attached drawings.

FIG. 1 is a schematic drawing illustrating a skeleton which constitutes a porous metallic material of the present invention;

FIG. 2 is a schematic perspective view and enlarged sectional view of a principal portion, illustrating a porous metallic plate material in accordance with an embodiment of the present invention;

FIG. 3 is a schematic perspective view and enlarged sectional view of a principal portion, illustrating the structure of a porous metallic plate material in accordance with another embodiment of the present invention;

FIG. 4 is a schematic perspective view and enlarged sectional view of a principal portion, illustrating the structure of a porous metallic plate material in accordance with a further embodiment of the present invention;

FIG. 5 is a schematic perspective view and enlarged sectional view of a principal portion, illustrating the structure of a porous metallic plate material in accordance with a still further embodiment of the present invention;

FIG. 6 is a drawing illustrating the sectional structure of an electrode of an alkaline secondary battery of the present invention;

FIG. 7 is a schematic drawing illustrating a skeleton which constitutes a conventional porous metallic material;

FIG. 8 is a drawing illustrating the sectional structure of an electrode of a conventional alkaline secondary battery;

FIG. 9A is a microphotograph showing a cross-section of a skeleton of a porous metallic material in accordance with the present invention;

FIG. 9B is a microphotograph showing a cross-section of a skeleton of a porous metallic material in accordance with a comparative example;

FIG. 10A is a microphotograph showing the appearance of a skeleton of a porous metallic material in accordance with the present invention; and

FIG. 10B is a microphotograph showing the appearance of a skeleton of a porous metallic material in accordance with a comparative example.

BEST MODE FOR CARRYING OUT THE INVENTION

The porous metallic material of the present invention can be produced through the steps of preparing a foamable slurry, forming, drying, degreasing, and sintering.

The foamable slurry, for example, containing a metal powder, a water-soluble resin binder, a foaming agent, a surfactant and water is first prepared. The type of the metal powder used is not limited, and, any metals and alloys which can be sintered, such as nickel, copper, iron, SUS, chromium, cobalt, gold and silver can be used. Nickel is generally used for producing an electrode of an alkaline secondary battery. The average particle size of the metal powder is not more than 500 um, preferably within the range of 0.5 to 100 μm. The porosity of the skeleton which constitutes the porous metallic material of the present invention can be adjusted by adjusting the average particle size of the metal powder. With an average particle size of 0.5 μm or less, the porosity is decreased in some cases. With an average particle size of 500 μm or more, the strength of the resultant porous sintered metal plate is excessively decreased. The content of the metal powder in the slurry is 5 to 80% (% by weight hereinafter), preferably 30 to 80%.

The water soluble resin binder helps to maintain the shape of the porous formed product when the slurry is dried. The water soluble resin binder also functions as a slurry viscosity modifier. Examples of such a water-soluble resin binder include methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose ammonium, ethyl cellulose, polyvinyl alcohol and the like. The content of the water-soluble resin binder is within the range of 0.5 to 20%, preferably within the range of 2 to 10%. With a content of less than 0.5%, the dry formed product has insufficient strength and cannot be easily handled. On the other hand, with a content of over 20%, the viscosity excessively increases, and forming thus becomes difficult.

The foaming agent may have the ability to form cells by generating gas. Therefore, a compound which generates a gas by decomposition at a predetermined temperature, or a volatile organic solvent can be selected as the foaming agent. Examples of volatile organic solvents include hydrocarbon organic solvents having 5 to 8 carbon atoms. Such organic solvents are liquid at room temperature, volatile, form micelles in the slurry by the action of the surfactant and vaporizes at room temperature or under heating to form fine cells. Examples of hydrocarbon organic solvents having 5 to 8 carbon atoms include pentane, neopentane, hexane, isohexane, isoheptane, benzene, octane, toluene and the like. The content of the foaming agent is 0.05 to 10%, preferably 0.5 to 5%. With a content of less than 0.05%, cells are not sufficiently generated, and the porosity is thus low. On the other hand, with a content of over 10%, the size of the cells formed in the formed product is increased due to an increase in the size of micelles, thereby decreasing the strength of the resultant formed product and sintered material. The foamable slurry can be prepared by the method of vigorously mixing a gas such as air in place of the use of the foaming agent.

The surfactant has the function to stabilize the foaming state to form micelles of the foaming agent. Examples of the surfactant include anionic surfactants such as alkyl benzenesulfonates, α-olefin sulfonates, alkyl sulfates, alkyl ether sulfates, alkane sulfonates and the like; and nonionic surfactants such as polyethylene glycol derivatives, polyhydric alcohol derivatives and the like. The content of the surfactant is within the range of 0.05 to 5%, preferably 0.5 to 3%. With a content of less than 0.05%, the formation of micelles is made unstable, and fine cells cannot be easily maintained. On the other hand, a content of over 5% causes no further effect.

The foamable slurry of the present invention may contain a plasticizer, a combustible agent for promoting cell formation other than the above components. The plasticizer is added for providing the formed product with plasticity. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol, polyethylene glycol, glycerin and the like; fats and oils such as sardine oil, rape seed oil, olive oil and the like; ethers such as petroleum ether and the like; esters such as diethyl phthalate, di-n-butyl phthalate, diethylhexyl phthalate, dioctyl phthalate, sorbitan monooleate, sorbitan trioleate, sorbitan palmitate, sorbitan stearate and the like. The content of the plasticizer is within the range of 0.1 to 15%, preferably 2 to 10%. A content of less than 0.1% causes insufficient plasticizing effect, while a content of over 15% causes insufficient strength of the formed product.

The combustible agent for promoting cell formation is added for promoting cell formation by disappearing in the burning of the dry formed product. Therefore, an agent which maintains the shape of a powder or fibers and which disappears in burning can be selected. Specifically, a powder having a particle size of about 0.1 to 200 μm, and fibers having a length of 200 μm or less, preferably about 30 to 120 μm, are preferred. Examples of materials for the combustible agent include pulp, cotton, yarn waste, corn starch, carboxylmethyl cellulose, water insoluble cellulose fibers, polyvinyl butyral fibers, polyvinyl fibers, acrylic fibers, polyethylene fibers and the like.

The foamable slurry of the present invention can be obtained by mixing the above components. In this case, the mixing order is not limited, but the foaming agent is preferably finally mixed in order to suppress foaming as much as possible during mixing.

The thus-prepared foamable slurry is then formed. The forming method is not limited, but a doctor blade method, a slip casting method and a coating method are preferable.

The formed product can be reinforced by using an reinforcing plate such as a plate or perforated plate preferably having a thickness of about 0.6 to 20 mm, or a net preferably of 20 to 200 mesh, which are made of a metal such as stainless steel, gold or copper, ceramic or carbon. For example, the foamable slurry can be coated on both sides of the reinforcing plate, or the reinforcing plate can be extruded together with the formed product so as to obtain a porous metallic plate material comprising the reinforcing plate positioned at the widthwise center of the formed product, as shown in FIGS. 3 to 5. Further, at least two reinforcing plates can be provided in a formed product at predetermined spaces therebetween, or a reinforcing plate can be provided on one or both sides of a formed product to obtain a porous metallic plate material.

In the foaming and drying (cell forming) step, the foaming agent is sufficiently foamed, and at the same time, the formed product is dried. In this step, foaming and drying can be carried out for sufficiently foaming the foaming agent at room temperature to 110° C. If one side or both sides of the formed product are heated at 150° to 300° C. by a far infrared heater immediately after forming, the vicinity of the surface of the formed product irradiated with far infrared rays is rapidly dried, and enlargement and growth of cells in the vicinity of the surface are suppressed, thereby obtaining the formed product having small pores formed on the surface side thereof, and large pores formed on the inside thereof. The formation of such a microporous surface layer increases strength. When a plate is formed, the plate thickness is preferably about 0.4 to 20 mm.

Since cracks easily occur in the surface of the formed product, if the formed product is dried at the same time as foaming, the foaming step is preferably performed before the drying step. Foaming is preferably performed in an atmosphere at a high humidity in order to prevent drying as much as possible. For example, with a slurry viscosity of 35000 cps or more, the humidity is at least 65%, preferably at least 80%. If the humidity is 65% or lower, the surface of the formed product might be cracked in drying. For example, when n-hexane is used as the foaming agent, the foaming temperature is 15° to 65° C., preferably 28 to 40° C. At the foaming temperature of 15° C. or lower, for example, at least 2 hours are required for foaming. At the foaming temperature of over 65° C., the foamed product is excessively foamed, and thus broken. The foaming time is generally within the range of 10 to 45 minutes.

The burning step preferably comprises two steps, i.e. a first step referred to as a degreasing step for volatilizing the organic material (binder), and a second step for sintering the metal powder. These steps can be continuously performed.

In the degreasing step, the formed product can be burned at a temperature of about 300° to 700° C. for 10 to 60 minutes in an atmosphere of air or a reducing gas such as hydrogen gas. In the sintering step, the formed product can be burned at a temperature of about 800° to 1400° C. for 20 to 120 minutes in a reducing atmosphere of ammonia cracked gas or hydrogen gas, under vacuum or in air in accordance with the type of the metal produced.

In this way, a spongelike porous metallic material having a large surface area and a three-dimensional network skeleton structure can be obtained. Since this porous metallic material has the three-dimensional network skeleton comprising a sintered metal powder, the skeleton itself is porous. The porosity of the skeleton is 10 to 60%. The surface area of the metallic material is thus very large, for example, the BET specific surface area is within the range of 300 to 11000 cm² /cm³. A foamed product having very small pores having a size of less than 100 μm can easily be obtained, as compared with a conventional method. Specifically, a foamed product having an average pore size within the range of 60 to 700 μm and a porosity of 80 to 99% by volume can be produced.

When the porous metallic material is elongated or thinned, if the specific surface area thereof is 1000 cm² /cm³ or more, it is easily deformed, chipped, cracked or broken in handling due to the insufficient strength. In this case, the porous metallic material preferably has an overall specific surface area of about 300 to 1000 cm² /cm³.

The porous metallic material obtained by the method of the present invention has the aforementioned characteristics, and can thus be usefully applied to, for example, an active material holding material of an electrode of an alkaline secondary battery, a hydrolytic electrode, a kerosene atomizing member of a petroleum heater, a magnetic shield packing, a gas expansion buffer of an air cushion using an explosive, a sound absorbing material, a hydrolytic filter of a clarifier, an electrostatic filter of an air clarifier, an oil mist filter for an engine exhaust gas, a deodorization catalyst of a combustion apparatus such as a petroleum stove, a filter of a high-temperature exhaust dust collector, a substrate of a composite material (CRM) having pores filled with aluminum under high pressure, an industrial catalyst, a carrier, etc.

When the porous metallic material of the present invention is used for an electrode of an alkaline secondary battery, an attempt can be made to increase the life of the alkaline secondary battery.

Although the spongelike porous metallic substrate having the skeleton comprising the microporous sintered metal, which constitutes an electrode of an alkaline secondary battery in accordance with the present invention, generally consists of Ni, the substrate material is not limited to Ni, and a metal or alloy having any composition can be used as long as it has excellent corrosion resistance and conductivity. The spongelike porous metallic substrate having the skeleton comprising the microporous sintered metal, which constitutes an electrode of an alkaline secondary battery in accordance with the present invention, preferably has an overall porosity of 80 to 99% (more preferably 95 to 99%), and a specific surface area of 300 to 1000 cm² /cm³ (more preferably 400 to 800 cm² /cm³).

When an electrode of an alkaline secondary battery of the present invention is formed by using the porous metallic material obtained by the aforementioned method, the spongelike porous metallic substrate has an excellent specific surface area of, for example, 300 to 1000 cm² /cm³, compared with a conventional porous metallic substrate comprising nickel foam and having a specific surface area of 40 cm² /cm³ at most.

Although the spongelike porous metallic substrate has pores having an average pore size of 60 to 700 μm, which is substantially the same as that of a conventional material, the amount of the active material contained in the electrode of the alkaline secondary battery of the present invention is 75 to 85 mg/cm³, which is superior to a conventional electrode of an alkaline secondary battery having a content of the active material of 65 mg/cm³ at most.

EXAMPLE 1

The porous metallic material of the present invention is described in detail below with reference to examples.

Various metal powders having the average particle sizes and compositions shown in Tables 1 and 2 were formed. As the organic solvent, the following solvents were used.

Neopentane (referred to as "A-1" hereinafter);

Hexane (referred to as "A-2" hereinafter);

Isohexane (A-3);

Heptane (A-4);

Isoheptane (A-5);

Benzene (A-6);

Octane (A-7); and

Toluene (A-8).

Commercial kitchen neutral synthetic detergents including nonionic surfactants such as polyethylene glycol derivatives, polyhydric alcohol derivatives and the like were used as the water-soluble resin binder:

Methyl cellulose (referred to as "B-1" hereinafter);

Hydroxypropylmethyl cellulose (referred to as "B-2" hereinafter);

Hydroxyethylmethyl cellulose (B-3);

Carboxymethyl cellulose ammonium (B-4);

Ethyl cellulose (B-5); and

Polyvinyl alcohol (B-6).

As the plasticizer, the following compounds were prepared:

Polyethylene glycol (referred to as "C-1" hereinafter);

Olive oil (referred to as "C-2" hereinafter);

Petroleum ether (C-3);

Di-n-butyl phthalate (C-4); and

Sorbitan monooleate (C-5).

These components were added to water in the mixing compositions shown in Tables 1 and 2 and mixed under ordinary conditions to prepare raw material mixtures (foamable slurry) 1a to 1p.

Each of the raw material mixtures was injected into a plaster mold having a cavity surface provided with a plurality of through microholes to form a molded product. The thus-obtained molded product was then subjected to pore formation, degreased and sintered under the conditions shown in Tables 3 and 4 to produce porous metallic materials 1 to 16 of the present invention which had the dimensions of 50 mm.O slashed. in diameter×100 mm in length.

For comparison, Ni was deposited to a thickness of 0.5 μm on one side (inner side) of a commercial polyurethane foam to provide the urethane foam with conductivity, and the urethane foam in this state was then dipped in a nickel sulfate aqueous solution and Ni electroplated at a cathode with a current density of 1 A/dm² to form Ni plated layers having an average thickness of 75 μm on the surfaces of the through holes of the polyurethane foam. The polyurethane foam was then burned by heating at a temperature of 1100° C. for 0.5 hour in a stream of hydrogen to produce a conventional porous metallic material having the dimensions of 50 mm.O slashed. in diameter×100 mm in length.

The overall porosity of each of the resultant various porous metallic materials was measured by an image analyzer, and the overall specific surface area was also measured by the BET method. The overall porosity of each of the porous metallic materials 1 to 16 of the present invention includes the porosity of the skeleton. Table 5 shows the averages of measurements obtained at 30 measurement points.

                                      TABLE 1                                      __________________________________________________________________________     COMPOSITION (Mass %)                                                                AVERAGE                                                                        PARTICLE                                                                             COMPOSITION                                                                            METAL                   WATER SOLUBLE                                                                            PLAS-                     TYPE SIZE (μm)                                                                         (wt %)  POWDER                                                                              ORGANIC SOLVENT                                                                           SURFACTANT                                                                             RESIN BINDER                                                                             TICIZER                                                                             WATER                __________________________________________________________________________     MIXED RAW MATERIAL                                                             1a   2     Ni      65   A-(2):2    1       B-(2):2.7 --   BAL.                 1b   9     Cu      65   A-(1):0.5  2.5     B-(3):3   --   BAL.                                         A-(2):1                                                1c   20    Cu-20% Ni                                                                              70   A-(4):1    0.06    B-(6):2   --   BAL.                 1d   185   Ni      32   A-(5):2    1       B-(1):0.5 --   BAL.                      9     Cu      32                      B-(2):1                                                                        B-(4):0.6                           1e   45    Ag      75   A-(3):2    1       B-(2):1.5 --   BAL.                                         A-(2):1.5          B-(3):2                                                     A-(7):5.5                                              1f   8     SUS430  32   A-(6):0.6  4.5     B-(5):19  --   BAL.                 1g   20    Au      75   A-(8):2.5  0.5     B-(2):2   --   BAL.                 1h   0.6   W       63   A-(7):2    1       B-(1):2.5 --   BAL.                      9     Cu      4                                                                2     Ni      1                                                           __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________     COMPOSITION (Mass %)                                                               AVERAGE                                                                        PARTICLE                                                                             COMPOSITION                                                                            METAL           SURFACT-                                                                             WATER SOLUBLE                          TYPE                                                                               SIZE (μm)                                                                         (wt %)  POWDER                                                                              ORGANIC SOLVENT                                                                           ANT   RESIN BINDER                                                                             PLASTICIZER                                                                            WATER                __________________________________________________________________________     MIXED RAW MATERIAL                                                             1i  2     Ni      65   A-(2):2    1     B-(2):2.7 C-(5):1 BAL.                 1j  10    Ni-15.5%                                                                               68   A-(2):1    1.5   B-(2):2   C-(1):2.5                              Cr-8% Fe-    A-(3):0.5                                                         0.8% Mn                                                              1k  8     Co-10% Ni-                                                                             52   A-(1):0.5  4.8   B-(4):2   C-(3):0.5                                                                              BAL.                           15% Cr       A-(7):2          B-(6):0.9 C-(4):1.4                                           A-(8):6.5                  C-(5):0.6                    1l  0.6   W       63   A-(7):2    1     B-(1):0.5 C-(1):0.5                                                                              BAL.                     9     Cu      4.5                   B-(2):0.5 C-(5):0.6                        3     Co      0.5                   B-(3):0.5                              1m  11    Ag-7.5% 31   A-(4):0.6  0.06  B-(5):19  C-(2):14.5                                                                             BAL.                           Cu                                                                   1n  185   Ni      32   A-(5):2    1     B-(3):2   C-(5):6.1                                                                              BAL.                     9     Cu      32                                                           1o  35    Ni-20% Cr                                                                              78   A-(2):1    0.5   B-(2):1.5 C-(4):1 BAL.                 1p  10    SUS304  60   A-(4):2.5  1.5   B-(2):2   C-(3):2 BAL.                 __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________               PORE FORMATION CONDITIONS                                            MIXED             TEM-                                                         RAW               PERA-    DEGREASING CONDITION                                                                             SINTERING CONDITION                   MATERIAL                                                                             ATMOS-  TURE                                                                               TIME ATMOS-                                                                              TEMPERATURE                                                                             TIME                                                                               ATMOS-                                                                              TEMPERATURE                                                                             TIME                TYPE                                                                               SYMBAL                                                                               PHERE   (°C.)                                                                       (min.)                                                                              PHERE                                                                               (°C.)                                                                            (min.)                                                                             PHERE                                                                               (°C.)                                                                            (min.)              __________________________________________________________________________     POROUS METALLIC MATERIAL OF THIS INVENTION                                     1   1a    AIR WITH 90%                                                                           60  120  AIR  500      30  HY-  1150     60                  2   1b    HUMIDITY                                                                               45  40        450          DROGEN                                                                              1030     120                 3   1c            30  15                          1150                         4   1d            25  30        500      60       1000     60                  5   1e            50  40                 15  AIR  910      300                 6   1f            20  30        450      240 HY-  1190     120                                                              DROGEN                            7   1g            50  25        500      30  AIR  1010     60                  8   1h            35  120  HY-  600      60  HY-  1200                                                    DROGEN            DROGEN                            __________________________________________________________________________

                                      TABLE 4                                      __________________________________________________________________________               PORE FORMATION CONDITIONS                                            MIXED             TEM-                                                         RAW               PERA-    DEGREASING CONDITION                                                                             SINTERING CONDITION                   MATERIAL                                                                             ATMOS-  TURE                                                                               TIME ATMOS-                                                                              TEMPERATURE                                                                             TIME                                                                               ATMOS-                                                                              TEMPERATURE                                                                             TIME                TYPE                                                                               SYMBAL                                                                               PHERE   (°C.)                                                                       (min.)                                                                              PHERE                                                                               (°C.)                                                                            (min.)                                                                             PHERE                                                                               (°C.)                                                                            (min.)              __________________________________________________________________________     POROUS METALLIC MATERIAL OF THIS INVENTION                                      9  1i    AIR WITH 90%                                                                           40  60   AIR  500      30  HY-  1300     180                 10  1j    HUMIDITY                           DROGEN        120                 11  1k            25  15        450          VAC- 1320                                                                      UUM                               12  1l            50  30                 15  HY-  1200     30                                                               DROGEN                            13  1m            60  60        550      120 AIR  920      120                 14  1n    ARGON   30  20        500      100 HY-  1050                                                                      DROGEN                            15  1o    NITROGEN         HY-  550      120      1300     180                                            DROGEN                                              16  1p            40  60   AIR  450      30                                    __________________________________________________________________________

                  TABLE 5                                                          ______________________________________                                               OVERALL SPECIFIC                                                                               OVERALL    POROSITY OF                                         SURFACE AREA    POROSITY   SKELETON                                      TYPE  (cm.sup.2 /cm.sup.2)                                                                           (%)        (%)                                           ______________________________________                                         POROUS METALLIC MATERIAL                                                       OF THIS INVENTION                                                              1     390             98.6       22                                            2     620             95         25                                            3     410             95         31                                            4     2800            82         52                                            5     350             97         21                                            6     1150            89         41                                            7     1200            88         33                                            8     310             97         11                                            9     420             96         25                                            10    630             95         33                                            11    2400            82         52                                            12    590             92         14                                            13    660             92         22                                            14    2900            81         54                                            15    710             93         23                                            16    880             92         31                                            CONVENTIONAL POROUS METALLIC                                                   MATERIAL (COMPARATIVE EXAMPLE 1)                                               41                95         --                                                ______________________________________                                    

The results shown in Table 5 reveal that all porous metallic materials 1 to 16 of the present invention have the skeleton comprising a porous sintered metal, as shown in FIG. 1, and that the porous sintered metal has a high porosity of 10 to 60%, and thus has an extremely high specific surface area, as compared with the conventional porous metallic material (Comparative Example 1) having a skeleton comprising a nonporous metallic hollow material, as shown in FIG. 7.

FIG. 9A is a microphotograph showing the cross-sectional structure of the skeleton of the porous metallic material 1 of the present invention. FIG. 10A is a microphotograph showing the appearance of the skeleton of the porous metallic material 1 of the present invention. The magnifications of FIGS. 9A and 10A are X400 and X300, respectively.

As shown in FIGS. 9A and 10A, the porous metallic material of the present invention has the skeleton which is comprised entirely of the porous sintered metal powder.

As described above, the porous metallic material of the present invention has a very large specific surface area, and thus exhibits excellent performance when applied to structural members of various machines and apparatus. It is thus possible to satisfactorily comply with the demands for increasing performance and output of various machines and apparatus and decreasing weights thereof.

Comparative Example 1

A spongelike resin was plated and then burned to obtain a porous metallic material comprising a skeleton having pores formed therein by burning, as shown in a schematic drawing of FIG. 7.

FIG. 9B shows the cross-sectional shape of the skeleton, and FIG. 10B shows the appearance of the skeleton. The magnifications of FIGS. 9B and 10B are X400 and X200, respectively.

As shown in FIGS. 9B and 10B, the skeleton of the porous metallic material obtained by the method in accordance with the comparative example is not solid and is hollow, and has no pore in the surface thereof.

As a result of measurement of the overall specific surface area and the overall porosity in the same manner as in Example 1, the porous metallic material had a specific surface area of 41 cm² /cm³ and a porosity of 95%, as shown in Table 5.

EXAMPLE 2

Description will now be made of an example in which a porous metallic material is produced so as to form pores in the surface thereof which are smaller than internal pores.

Various metal powders having the average particle sizes and compositions shown in Tables 6 and 7, an organic solvent, the above-described commercial kitchen neutral synthetic detergents as surfactants, a water-soluble resin binder, a plasticizer were prepared, added to water in the mixing compositions shown in Tables 6 and 7 and mixed under ordinary conditions to prepare mixtures 2a to 2p.

As the organic solvent, neopentane A-(1)!, hexane A-(2)!, isohexane A-(3)!, heptane A-(4)!, isoheptane A-(5)!, benzene A-(6)!, octane A-(7)! and toluene A-(8)! were used. As the water-soluble resin binder, methyl cellulose B-(1)!, hydroxypropylmethyl cellulose B-(2)!, hydroethylmethyl cellulose B-(3)!, carboxymethyl cellulose ammonium B-(4)!, ethyl cellulose B-(5)!, and polyvinyl alcohol B-(6)! were used. As the plasticizer, polyethylene glycol C-(1)!, olive oil C-(2)!, petroleum ether C-(3)!, n-butyl phthalate C-(4)!, sorbitan monooleate C-(5)! and glycerin were used.

Each of the mixtures 2a to 2p was coated to a predetermined thickness on a carrier sheet by a known doctor blade method to form a plate. One side of the thus-formed plate was irradiated with far infrared rays by a far infrared heating device at a predetermined heater surface temperature within the range of 150° to 300° for a predetermined time within the range of 30 to 300 seconds, and then subjected to pore formation under the conditions shown in Table 8. The plate was degreased by being held at a temperature of 500° C. for 2 hours in air, and then sintered under the conditions shown in Table 8, to produce each of porous metallic plates 17 to 32 of the present invention each having the thickness shown in Table 9 and a porous surface layer on one side thereof.

For comparison, Ni was deposited to a thickness of 0.5 μm on one side of a commercial polyurethane foam plate to provide the polyurethane foam with conductivity, and the polyurethane foam plate in this state was dipped in a nickel sulfate aqueous solution to perform Ni electroplating thereon at a cathode with a current density of 0.5 A/dm², to form Ni plated layers having an average thickness of 50 μm on the surfaces of the through holes of the polyurethane foam. The polyurethane foam was then burned by heating at 1100° C. for 0.5 hour in a stream of hydrogen to produce a conventional porous metallic plate having a thickness of 1.6 mm.

The overall porosity and the overall specific surface area of each of the resultant porous metallic plate materials 17 to 32 of the present invention and the conventional porous metallic plate were measured by using an image analyzer and the BET method, respectively. The porosity of the skeleton which constitutes each of the porous metallic plate materials, the thickness of the porous surface layer, and the sizes of the pores formed by the skeleton in the porous surface layer and the central portion of the plate material were further measured. Table 9 show averages of the measurements obtained at 30 measurement points.

                                      TABLE 6                                      __________________________________________________________________________     COMPOSITION (Mass %)                                                               AVERAGE                                                                        PARTICLE                                                                             COMPOSITION                 SURFACT-                                                                             WATER SOLUBLE                                                                            PLAS-                                                                               WAT-                TYPE                                                                               SIZE (μm)                                                                         (wt %)  METAL POWDER                                                                            ORGANIC SOLVENT                                                                           ANT   RESIN BINDER                                                                             TICIZER                                                                             ER                  __________________________________________________________________________     MIXED RAW MATERIAL                                                             2a  9     Ni      50       A-1:0.6    2.5   B-4:4     --   BAL.                                                            B-5:1                              2b  40    Cu      50       A-2:0.5    0.07  B-1:5     --   BAL.                2c  460   Cu-10% Ni                                                                              60       A-6:0.5    4.8   B-3:0.8   --   BAL.                                           A-8:1                                               2d  2     Ni      25       A-7:0.07   2     B-1:2     --   BAL.                    40    Cu      25                        B-3:2                              2e  20    Au      78       A-2:5      3     B-2:7     --   BAL.                                           A-4:2.5                                                                        A-7:2                                               2f  40    Ag      70       A-4:0.4    4     B-6:2     --   BAL.                2g  110   Fe      37       A-5:5      2     B-4:15    --   BAL.                    35    Cr      9                                                                9     Ni      4                                                            2h  110   Fe      3        A-3:0.3    0.5   B-1:10    --   BAL.                    65    Co      3        A-4:0.7          B-2:4                                                                          B-5:5                              __________________________________________________________________________

                                      TABLE 7                                      __________________________________________________________________________     COMPOSITION (Mass %)                                                               AVERAGE                                                                        PARTICLE                                                                             COMPOSITION                 SURFACT-                                                                             WATER SOLUBLE                                                                            PLAS-                                                                               WAT-                TYPE                                                                               SIZE (μm)                                                                         (wt %)  METAL POWDER                                                                            ORGANIC SOLVENT                                                                           ANT   RESIN BINDER                                                                             TICIZER                                                                             ER                  __________________________________________________________________________     MIXED RAW MATERIAL                                                             2i  12    SUS310S 40       A-2:0.2    2     B-1:9.5   C-1:3                                                                               BAL.                                           A-4:0.2          B-3:0.5                                                       A-7:0.2                                             2j  108   SUS304  40       A-2:0.8    0.08  B-2:5     C-3:1.5                                                                             BAL.                                                                      C-5:1                    2k  460   Cu-10% Ni                                                                              75       A-4.3      2     B-1:0.8   C-3:0.2                                                                             BAL.                2l  13    Ni      24       A-3.0      1     B-3:5     C-1:9                                                                               BAL.                    0.6   Cr      6                                   C-4:3                                                                          C-5:2                    2m  15    Co-10% Ni-                                                                             45       A-5:0.08   1.5   B-4:4     C-2:0.1                                                                             BAL.                          15% Cr                                                               2n  12    Co-10% Ni                                                                              6        A-4:0.6    1.5   B-2:8     C-2.5                                                                               BAL.                          20% Cr-15%                                                                             6                         B-4:0.5   C-3:5                              W                                 B-6:0.5                            2o  110   Fe      25       A-1:0.3    5     B-5:5     C-4:1                                                                               BAL.                    65    Co      13.5     A-6:0.3                                                 13    Ni      7.5                                                          2p  12    Ni      45       A-8:0.7    0.6   B-6:6     C-5:6                                                                               BAL.                __________________________________________________________________________

                                      TABLE 8                                      __________________________________________________________________________               PORE FORMATION                                                       MIXED     CONDITION      SINTERING CONDITION                                       RAW         TEMPE-          TEMPE-                                             MATERIAL                                                                             ATMOS-                                                                               RATURE                                                                              TIME                                                                               ATMOS- RATURE                                                                              TIME                                      TYPE                                                                               SYMBOL                                                                               PHERE (°C.)                                                                        (min.)                                                                             PHERE  (°C.)                                                                        (min.)                                    __________________________________________________________________________     POROUS METALLIC PLATE MATERIAL OF THIS INVENTION                               17  2a    AIR   25   90  HYDROGEN                                                                              1200 60                                        18  2b          30              1000                                           19  2c          105  20                                                        20  2d          25   90         1060 120                                       21  2e          5    180 VACUUM 1030 60                                        22  2f                          900  240                                       23  2g    NITROGEN                                                                             10   120 HYDROGEN                                                                              1250 30                                        24  2h    ARGON                 1300 60                                        25  2i    AIR   30   90         1250                                           26  2j                                                                         27  2k          10   120        1000                                           28  2l    ARGON 20   90         1250                                           29  2m    AIR   105  20  VACUUM                                                30  2n                          1350                                           31  2o          25   90  HYDROGEN                                                                              1250                                           32  2p                          1100                                           __________________________________________________________________________

                                      TABLE 9                                      __________________________________________________________________________                POROUS SURFACE                                                                 LAYER      AVERAGE                                                      THICKNESS   AVERAGE                                                                              PORE SIZE                                                                             POROSITY                                              OF PLATE                                                                              THICK-                                                                              PORE  OF CENTRAL                                                                            OF    OVERALL                                                                              OVERALL SPECIFIC                          MATERIAL                                                                              NESS SIZE  PORTION OF                                                                            SKELETON                                                                             POROSITY                                                                             SURFACE AREA                          TYPE                                                                               (mm)   (mm) (mm)  PLATE  (%)   (%)   (cm.sup.2 /cm.sup.2)                  __________________________________________________________________________     POROUS METALLIC PLATE MATERIAL OF THIS INVENTION                               17     2.1 0.30 0.11  0.46   40    98    4100                                  18     4.9 0.51 0.11  0.51   35    88    1700                                  19     42.1                                                                               3.2  0.24  0.92   55    81    1000                                  20     10.8                                                                               1.2  0.21  0.47   49    80    1100                                  21     3.3 0.22 0.07  0.39   33    85    3200                                  22     5.5 0.51 0.10  0.40   30    94    2600                                  23     18.1                                                                               0.60 0.26  0.61   41    92    2000                                  24     17.1                                                                               0.41 0.25  0.66   34    82    1700                                  25     3.0 0.45 0.14  0.51   32    87    3800                                  26     9.5 1.2  0.11  0.49   45    80    1500                                  27     16.9                                                                               3.1  0.23  0.97   54    88    1050                                  28     4.0 0.9  0.09  0.38   36    97    5400                                  29     2.1 0.70 0.09  0.41   39    83    2700                                  30     1.6 0.34 0.20  0.39   40    86    2900                                  31     9.0 1.0  0.26  0.71   41    88    2200                                  32     39.8                                                                               2.2  0.20  0.59   32    80    3200                                  CONVENTIONAL POROUS METALLIC PLATE MATERIAL                                    1.5        --   --    0.70   --    95    51                                    __________________________________________________________________________

The results shown in Table 9 reveal that all porous metallic plate materials 17 to 32 of the present invention have the skeleton which comprises the porous sintered metal, as shown in FIG. 1, and which has a high porosity of 30 to 60%, and thus have extremely high specific surface areas, as compared with the conventional porous metallic plate having the skeleton comprising a nonporous metal, as shown in FIG. 7.

As described above, the porous metallic plate materials of the present invention have very high specific surface areas and maintain strength due to the porous surface layers. The porous metallic plate materials thus exhibit excellent performance when applied to structural members of various machines and apparatus, and can satisfactorily comply with the demands for increasing performance and output of various machines and apparatus.

EXAMPLE 3

Description will now be made of an example in which a porous metallic plate is produced so as to form surface pores smaller than internal pores.

Various metal powders having the average particle sizes and compositions shown in Tables 10 and 11, an organic solvent, the above commercial kitchen neutral synthetic detergents as surfactants, a water-soluble resin binder, a plasticizer were prepared, added to water in the mixing compositions shown in Tables 10 and 11, and mixed under ordinary conditions to prepare mixtures 3a to 3p.

As the organic solvent, neopentane (A-1), hexane (A-2), isohexane (A-3), heptane (A-4), isoheptane (A-5), benzene (A-6), octane (A-7) and toluene (A-8) were used. As the water-soluble resin binder, methyl cellulose (B-1), hydroxypropylmethyl cellulose (B-2), hydroxyethylmethyl cellulose (B-3), carboxymethyl cellulose ammonium (B-4), ethyl cellulose (B-5) and polyvinyl alcohol (B-6) were used. As the plasticizer, polyethylene glycol (C-1), olive oil (C-2), petroleum ether (C-3), di-n-butyl phthalate (C-4) and sorbitan monooleate (C-5) were used.

Each of the mixtures 3a to 3p was coated to a predetermined thickness on a carrier sheet by the known doctor blade method to form a plate. One side of the thus-formed plate was irradiated with far infrared rays by a far infrared heating device at a predetermined heater surface temperature within the range of 150° to 300° for a predetermined time within the range of 30 to 300 seconds, and then subjected to pore formation under the conditions shown in Table 12. The plate was degreased by being held at a temperature of 500° C. for 2 hours in air, and then sintered under the conditions shown in Table 12, to produce each of porous metallic plate materials 33 to 48 of the present invention each having the thickness shown in Table 13 and a porous surface layer on one side thereof.

For comparison, Ni was deposited to a thickness of 0.5 μm on one side of a commercial polyurethane foam plate to provide the polyurethane foam with conductivity, and the polyurethane foam plate in this state was dipped in a nickel sulfate aqueous solution to perform Ni electroplating thereon at a cathode with a current density of 0.5 A/dm², to form Ni plated layers having an average thickness of 50 μm on the surfaces of the through holes of the polyurethane foam. The polyurethane foam was then burned by heating at 1100° C. for 0.5 hour in a stream of hydrogen to produce a conventional porous metallic plate material having a thickness of 1.6 mm.

The overall porosity and the overall specific surface area of each of the resultant porous metallic plate materials 17 to 32 of the present invention and the conventional porous metallic plate material were measured by using an image analyzer and the BET method, respectively. The porosity of the skeleton which constitutes each of the porous metallic plate materials, the thickness of the porous surface layer, and the sizes of the pores formed, by the skeleton, in the porous surface layer and the central portion of the plate material were further measured. Table 13 shows the averages of the measurements obtained at 30 measurement points.

                                      TABLE 10                                     __________________________________________________________________________     COMPOSITION (Mass %)                                                               AVERAGE                                                                        PARTICLE                                                                             COMPOSITION                                                                            METAL                    WATER SOLUBLE                                                                            PLAS-                     TYPE                                                                               SIZE (μm)                                                                         (wt %)  POWDER                                                                               ORGANIC SOLVENT                                                                           SURFACTANT                                                                             RESIN BINDER                                                                             TICIZER                                                                             WATER                __________________________________________________________________________     MIXED RAW MATERIAL                                                             3a  2     Ni      65    A-(2):2    1       B-(2):2.7 --   BAL.                 3b  9     Cu      65    A-(1):0.5  2.5     B-(3):3   --   BAL.                                         A-(2):1                                                3c  20    Cu-20% Ni                                                                              70    A-(4):1    0.06    B-(6):2   --   BAL.                 3d  185   Ni      32    A-(5):2    1       B-(1):0.5 --   BAL.                     9     Cu      32                       B-(2):1                                                                        B-(4):0.6                           3e  45    Ag      75    A-(3):2    1       B-(2):1.5 --   BAL.                                         A-(2):1.5  B-(3):2                                                             A-(7):5.5                                              3f  8     SUS430  32    A-(6):0.6  4.5     B-(5):19  --   BAL.                 3g  20    Au      75    A-(8):2.5  0.5     B-(2):2   --   BAL.                 3h  0.6   W       63    A-(7):2    1       B-(1):2.5 --   BAL.                     9     Cu      4                                                                2     Ni      1                                                            __________________________________________________________________________

                                      TABLE 11                                     __________________________________________________________________________     COMPOSITION (Mass %)                                                               AVERAGE                                                                        PARTICLE                                                                             COMPOSITION                                                                            METAL           SURFACT-                                                                             WATER SOLUBLE                          TYPE                                                                               SIZE (μm)                                                                         (wt %)  POWDER                                                                              ORGANIC SOLVENT                                                                           ANT   RESIN BINDER                                                                             PLASTICIZER                                                                            WATER                __________________________________________________________________________     MIXED RAW MATERIAL                                                             3i  2     Ni      65   A-(2):2    1     B-(2):2.7 C-(6):1 BAL.                 3j  10    Ni-15.5%                                                                               68   A-(2):1    1.5   B-(2):2   C-(1):2.5                                                                              BAL.                           Cr-8% Fe-    A-(3):0.5                                                         0.8% Mn                                                              3k  8     Co-10% Ni                                                                              52   A-(1):0.5  4.8   B-(4):2   C-(3):0.5                                                                              BAL.                           15% Cr       A-(7):2          B-(6):0.9 C-(4):1.4                                           A-(8):6.5                  C-(5):0.6                    3l  0.6   W       63   A-(7):2    1     B-(1):0.5 C-(1):0.5                                                                              BAL.                     9     Cu      4.5                   B-(2):0.5 C-(5):0.5                        3     Co      0.5                   B-(3):0.5                              3m  11    Ag-7.5% 31   A-(4):0.6  0.06  B-(5):19  C-(2):14.5                                                                             BAL.                           Cu                                                                   3n  185   Ni      32   A-(5):2    1     B-(3):2   C-(5):6.1                                                                              BAL.                     9     Cu      32                                                           3o  35    Ni-20% Cr                                                                              78   A-(2):1    0.5   B-(2):1.5 C-(4):1 BAL.                 3p  10    SUS430  60   A-(4):2.5  1.5   B-(2):2   C-(3):2 BAL.                 __________________________________________________________________________

                                      TABLE 12                                     __________________________________________________________________________               PORE FORMATION                                                       MIXED     CONDITION     SINTERING CONDITION                                        RAW        TEMPE-          TEMPE-                                              MATERIAL                                                                             ATMOS-                                                                              RATURE                                                                              TIME                                                                               ATMOS- RATURE                                                                              TIME                                       TYPE                                                                               SYMBOL                                                                               PHERE                                                                               (°C.)                                                                        (min.)                                                                             PHERE  (°C.)                                                                        (min.)                                     __________________________________________________________________________     POROUS METALLIC PLATE MATERIAL OF THIS INVENTION                               33  3a    AIR  40   60  HYDROGEN                                                                              1300 240                                        34  3b         45   40         1030 120                                        35  3c         30   15         1150                                            36  3d         25   30         1000 60                                         37  3e         50   40  AIR    910  300                                        38  3f         20   30  HYDROGEN                                                                              1190 120                                        39  3g         50   25  AIR    1010 60                                         40  3h         35   120 HYDROGEN                                                                              1200                                            41  3i         40   60         1300 180                                        42  3j                              120                                        43  3k         25   15  VACUUM 1320                                            44  3l         50   30  HYDROGEN                                                                              1200 30                                         45  3m         60   60  AIR    920  120                                        46  3n         30   20  HYDROGEN                                                                              1050                                            47  3o                         1300 180                                        48  3p         40   60                                                         __________________________________________________________________________

                                      TABLE 13                                     __________________________________________________________________________                POROUS SURFACE                                                                 LAYER      AVERAGE                                                      THICKNESS   AVERAGE                                                                              PORE SIZE                                                                             POROSITY                                              OF PLATE                                                                              THICK-                                                                              PORE  OF CENTRAL                                                                            OF    OVERALL                                                                              OVERALL SPECIFIC                          MATERIAL                                                                              NESS SIZE  PORTION OF                                                                            SKELETON                                                                             POROSITY                                                                             SURFACE AREA                          TYPE                                                                               (mm)   (mm) (mm)  PLATE  (%)   (%)   (cm.sup.2 /cm.sup.2)                  __________________________________________________________________________     POROUS METALLIC PLATE MATERIAL OF THIS INVENTION                               33  2.2    0.30 0.10  0.50   22    96    400                                   34  5.1    0.50 0.11  0.52   25    94    640                                   35  42.3   3.2  0.23  0.90   31    97    430                                   36  11.0   1.2  0.21  0.50   52    81    2900                                  37  3.5    0.23 0.07  0.40   21    96    360                                   38  5.7    0.51 0.10  0.58   41    87    1200                                  39  18.3   0.60 0.25  0.81   33    88    1200                                  40  17.4   0.41 0.24  0.62   11    97    310                                   41  3.2    0.42 0.14  0.54   25    94    440                                   42  9.8    1.2  0.11  0.52   33    94    630                                   43  17.2   3.1  0.23  0.97   52    80    2450                                  44  4.4    0.9  0.08  0.38   14    88    670                                   45  2.5    0.70 0.09  0.41   22    87    820                                   46  1.8    0.34 0.20  0.40   54    80    2900                                  47  9.2    1.0  0.25  0.80   23    92    730                                   48  39.8   2.2  0.20  0.61   31    91    900                                   CONVENTIONAL POROUS METALLIC PLATE MATERIAL                                    1.0        --   --    0.70   --    95    51                                    __________________________________________________________________________

The results shown in Table 13 reveal that all porous metallic plate materials 33 to 48 of the present invention have the skeleton which comprises the porous sintered metal, as shown in FIGS. 1 and 2, and which has a high porosity of 10 to 60%, and thus have extremely high specific surface areas, as compared with the conventional porous metallic plate material having the skeleton comprising a nonporous metal, as shown in FIG. 7.

As described above, the porous metallic plate materials of the present invention have very high specific surface areas and maintain strength due to the porous surface layers. The porous metallic plate materials thus exhibit excellent performance when applied to structural members of various machines and apparatus, and can satisfactorily comply with the demands for increasing performance and output of various machines and apparatus.

EXAMPLE 4

A porous metallic plate material reinforced by a reinforcing metallic plate of the present invention is described in detail with reference to an example.

Various metal powders having the average particle sizes and compositions shown in Tables 14 and 15, an organic solvent, the above commercial kitchen neutral synthetic detergents as surfactants, a water-soluble resin binder and a plasticizer were prepared, added to water in the compositions shown in Tables 14 and 15, and mixed under ordinary conditions to prepare mixtures 4a to 4p.

As the organic solvent, neopentane (A-1), hexane (A-2), isohexane (A-3), heptane (A-4), isoheptane (A-5), benzene (A-6), octane (A-7) and toluene (A-8) were used. As the water-soluble resin binder, methyl cellulose (B-1), hydroxypropylmethyl cellulose (B-2), hydroxyethylmethyl cellulose (B-3), carboxymethyl cellulose ammonium (B-4), ethyl cellulose (B-5) and polyvinyl alcohol (B-6) were used. As the plasticizer, polyethylene glycol (C-1), olive oil (C-2), petroleum ether (C-3), di-n-butyl phthalate (C-4), and sorbitan monooleate (C-5) were used.

Reinforcing metal plates A to E respectively comprising the materials and having thicknesses (mesh) and shapes shown in Table 16 were prepared.

A container was charged with each of mixtures 4a to 4p, and the reinforcing metallic plates A to E was dipped in the mixture in the combinations shown in Tables 17 and 18. The reinforcing metallic plate was drawn out from a slit having a predetermined width and provided in the container to form a plate comprising the reinforcing metallic plate at the center in the direction of the thickness thereof. The thus-formed plate was subjected to pore formation under the conditions shown in Table 17 and 18, degreased by being held at a temperature of 500° C. for 2 hours in air, and then sintered under the conditions shown in Tables 17 and 18 to produce porous metallic plate materials 49 to 64 each having the thickness shown in Table 19 and any one of the structures shown in a schematic perspective view and an enlarged sectional view of a principal portion of FIGS. 3 to 5.

For comparison, Ni was deposited to a thickness of 0.5 μm on one side (inner side) of a commercial polyurethane foam plate to provide the polyurethane foam with conductivity, and the polyurethane foam plate in this state was dipped in a nickel sulfate aqueous solution to perform Ni electroplating thereon at a cathode with a current density of 1 A/dm², to form Ni plated layers having an average thickness of 75 μm on the surfaces of the through holes of the polyurethane foam. The polyurethane foam was then burned by heating at 1100° C. for 0.5 hour in a stream of hydrogen to produce a conventional porous metallic plate material having a thickness of 3 mm.

The overall porosity and the overall specific surface area of each of the resultant porous metallic plate materials 49 to 64 of the present invention and the conventional porous metallic plate material were measured by using an image analyzer and the BET method, respectively. The porosity of the skeleton comprising a porous sintered metal which constitutes each of the porous metallic plate materials was further measured. Table 19 show the averages of the measurements obtained at 30 measurement points.

                                      TABLE 14                                     __________________________________________________________________________     COMPOSITION (Mass %)                                                               AVERAGE                                                                        PARTICLE                                                                             COMPOSITION                                                                            METAL                    WATER SOLUBLE                                                                            PLAS-                     TYPE                                                                               SIZE (μm)                                                                         (wt %)  POWDER                                                                               ORGANIC SOLVENT                                                                           SURFACTANT                                                                             RESIN BINDER                                                                             TICIZER                                                                             WATER                __________________________________________________________________________     MIXTURE                                                                        4a  9     Ni      50    A-1:0.6    2.5     B-4:4     --   BAL.                                                            B-5:1                               4b  40    Cu      50    A-2:0.5    0.07    B-1:5     --   BAL.                 4c  460   Cu-10% Ni                                                                              60    A-6:0.5    4.8     B-3:0.6   --   BAL.                                         A-8:1                                                  4d  2     Ni      25    A-7:0.07   2       B-1:2     --   BAL.                     40    Cu      25                       B-3:2                               4e  20    Au      78    A-2:5      3       B-2:7     --   BAL.                                         A-4:2.5                                                                        A-7:2                                                  4f  40    Ag      70    A-4:0.4    4       B-6:2     --   BAL.                 4g  110   Fe      37    A-5:5      2       B-4:15    --   BAL.                     35    Cr      9                                                                9     Ni      4                                                            4h  110   Fe      3     A-3:0.3    0.5     B-1:10    --   BAL.                     65    Co      3     A-4:0.7            B-2:4                                                                          B-5:5                               __________________________________________________________________________

                                      TABLE 15                                     __________________________________________________________________________     COMPOSITION (Mass %)                                                               AVERAGE                                                                        PARTICLE                                                                             COMPOSITION                                                                            METAL           SURFACT-                                                                             WATER SOLUBLE                          TYPE                                                                               SIZE (μm)                                                                         (wt %)  POWDER                                                                              ORGANIC SOLVENT                                                                           ANT   RESIN BINDER                                                                             PLASTICIZER                                                                            WATER                __________________________________________________________________________     MIXTURE                                                                        4i  12    SUS310S 40   A-2:0.2    2     B-1:9.5   C-1:3   BAL.                                        A-4:0.2          B-3:9.5                                                       A-7:0.2                                                 4j  108   SUS304  40   A-2:0.8    0.08  B-2:5     C-3:1.5 BAL.                                                                   C-5:1                        4k  460   Cu-10% Ni                                                                              75   A-4:3      2     B-1:0.8   C-3:0.2 BAL.                 4l  13    Ni      24   A-3.9      1     B-3:5     C-1:9   BAL.                     0.6   Cr      6                               C-4:8                                                                          C-5:2                        4m  15    Co-10% Ni                                                                              45   A-5:0.08   1.5   B-4:4     C-2:0.1 BAL.                           -15% Cr                                                              4n  12    Co-10% Ni                                                                              6    A-4:0.6    1.5   B-2:8     C-2:5   BAL.                           -20% Cr-15                    B-4:0.5   C-3:5                                  % W                           B-6:0.5                                4o  110   Fe      25   A-1:0.3    5     B-5:5     C-4:1   BAL.                     65    Co      13.5 A-6:0.3                                                     13    Ni      7.5                                                          4p  12    Ni      45   A-8:0.7    0.6   B-6:6     C-5:6   BAL.                 __________________________________________________________________________

                                      TABLE 16                                     __________________________________________________________________________               THICKNESS OR                                                         TYPE                                                                               MATERIAL                                                                             PARTICLE SIZE                                                                           SHAPE                                                       __________________________________________________________________________     REINFORCING METALLIC PLATE MATERIAL                                            A   Ni    48 mesh  WIRE CLOTH HAVING A WIRE DIAMETER OF 0.5 m                  B   Cu    0.3 m    PARFORATED PLATE IN WHICH HOLES HAVING A DIAMETER OF 1                         m                                                                              ARE FORMED WITH A PITCH 1.8 m                               C   Ni    0.1 mm   PLATE MATERIAL                                              D   Au    100 mesh WIRE CLOTH HAVING A WIRE DIAMETER OF 0.1 m                  E   SUS316L                                                                              0.3 m    PARFORATED PLATE IN WHICH HOLES HAVING A DIAMETER OF 1                         mm                                                                             ARE FORMED WITH A PITCH 1.8 mm                              __________________________________________________________________________

                                      TABLE 17                                     __________________________________________________________________________               REINFORCING                                                          MIXED     METALLIC                                                             RAW       PLATE   PORE FORMATION CONDITION                                                                          SINTERING CONDITION                           MATERIAL                                                                             MATERIAL                                                                               ATMOS-                                                                               TEMPERATURE                                                                             TIME                                                                               ATMOS- TEMPERATURE                                                                             TIME                      TYPE                                                                               SYMBOL                                                                               SYMBOL  PHERE (°C.)                                                                            (min.)                                                                             PHERE  (°C.)                                                                            (mm)                      __________________________________________________________________________     POROUS METALLIC MATERIAL OF THIS INVENTION                                     49  4a    A       AIR   25       90  HYDROGEN                                                                              1200     60                        50  4b    B             30                  1000                               51  4c    B             105      20                                            52  4d    A             25       90         1060     120                       53  4e    D             5        180 VACUUM 1030     60                        54  4f    D             10       120        900      240                       55  4g    E       NITROGEN           HYDROGEN                                                                              1250     30                        56  4h    E       ARGON                     1300     60                        __________________________________________________________________________

                                      TABLE 18                                     __________________________________________________________________________               REINFORCING                                                          MIXED     METALLIC                                                             RAW       PLATE   PORE FORMATION CONDITION                                                                         SINTERING CONDITION                            MATERIAL                                                                             MATERIAL                                                                               ATMOS-                                                                              TEMPERATURE                                                                             TIME                                                                               ATMOS- TEMPERATURE                                                                             TIME                       TYPE                                                                               SYMBOL                                                                               SYMBOL  PHERE                                                                               (°C.)                                                                            (min.)                                                                             PHERE  (°C.)                                                                            (mm)                       __________________________________________________________________________     POROUS METALLIC MATERIAL OF THIS INVENTION                                     57  4i    E       AIR        30 90  HYDROGEN                                                                              1250     60                         58  4j    E                                                                    59  4k    B                  10 120        1000                                60  4l    A       ARGON      20 90         1250                                61  4m    E       AIR        105                                                                               20  VACUUM                                     62  4n    E                                1350                                63  4o    C                  25 90  HYDROGEN                                                                              1250                                64  4p    C                                1100                                __________________________________________________________________________

                  TABLE 19                                                         ______________________________________                                                         OVERALL                                                                        SPECIFIC                                                             THICK-    SURFACE   OVERALL  POROSITY OF                                       NESS      AREA      POROSITY SKELETON                                    TYPE  (mm)      (cm.sup.2 /cm.sup.2)                                                                     (%)      (%)                                         ______________________________________                                         POROUS METALLIC PLATE MATERIAL OF THIS INVENTION                               49    2.2       4200      92       40                                          50    3.0       1800      90       35                                          51    6.8       1000      84       55                                          52    4.2       10500     81       49                                          53    0.6       3100      88       33                                          54    0.8       2700      94       30                                          55    1.9       2100      93       41                                          56    2.8       1900      82       34                                          57    10.1      4000      88       32                                          58    18.8      1500      81       45                                          59    3.1       1100      87       54                                          60    2.2       5500      97       36                                          61    5.0       2900      84       39                                          62    3.1       3000      88       40                                          63    0.8       2200      89       41                                          64    0.9       3300      80       32                                          CONVENTIONAL POROUS METALLIC PLATE MATERIAL                                    3.0         41        95         --                                            ______________________________________                                    

The results shown in Table 19 reveal that all porous metallic bodies which constitute the porous metallic plate materials 49 to 64 of the present invention have the skeleton which comprises the porous sintered metal, as shown in FIG. 1, and which has a high porosity of 30 to 60%, and that the porous metallic plate materials thus have extremely high specific surface areas, as compared with the conventional porous metallic plate material having the skeleton comprising a nonporous metal, as shown in FIG. 7.

As described above, the porous metallic plate materials of the present invention have very high specific surface areas and maintain strength due to the porous surface layers. The porous metallic plate materials thus exhibit excellent performance when applied to structural members of various machines and apparatus, and can satisfactorily comply with the demands for increasing performance and output of various machines and apparatus.

EXAMPLE 5

Description will now be made of another example of a porous metallic plate material reinforced by a reinforcing plate material of the present invention.

Various metal powders having the average particles sizes and compositions shown in Tables 20 and 21, an organic solvent, the above commercial kitchen neutral synthetic detergents as surfactants, a water-soluble resin binder and a plasticizer were prepared, added to water in the compositions shown in Tables 20 and 21, and mixed under ordinary conditions to prepare mixtures 5a to 5p.

As the organic solvent, neopentane A-(1)!, hexane A-(2)!, isohexane A-(3)!, heptane A-(4)!, isoheptane A-(5)!, benzene A-(6)!, octane A-(7)! and toluene A-(8)! were used. As the water-soluble resin binder, methyl cellulose B-(1)!, hydroxypropylmethyl cellulose B-(2)!, hydroxyethylmethyl cellulose B-(3)!, carboxymethyl cellulose ammonium B-(4)!, ethyl cellulose B-(5)! and polyvinyl alcohol B-(6)! were used. As the plasticizer, polyethylene glycol C-(1)!, olive oil C(2)!, petroleum ether C-(3)!, di-n-butyl phthalate C(4)!, and sorbitan monooleate C-(5)! were used.

Reinforcing metal plates A to E respectively comprising the materials and having thicknesses (mesh) and shapes shown in Table 22 were prepared.

A container was charged with each of mixtures 5a to 5p, and each of the reinforcing metallic plates A to E was dipped in the mixture in the combinations shown in Tables 23 and 24. The reinforcing metallic plate was drawn out from a slit having a predetermined width and provided in the container to form a plate comprising the reinforcing metallic plate at the center in the direction of the thickness thereof. The thus-formed plate was subjected to pore formation, degreased, and then sintered under the conditions shown in Table 23 and 24 to produce porous metallic plate materials 65 to 80 having the thicknesses shown in Table 25 and each of the structures shown in a schematic perspective view and an enlarged sectional view of a principal portion of FIGS. 3 to 5.

For comparison, Ni was deposited to a thickness of 0.5 μm on one side (inner side) of a commercial polyurethane foam plate to provide the polyurethane foam with conductivity, and the polyurethane foam plate in this state was dipped in a nickel sulfate aqueous solution to perform Ni electroplating thereon at a cathode with a current density of 1 A/dm², to form Ni plated layers having an average thickness of 75 μm on the surfaces of the through holes of the polyurethane foam. The polyurethane foam was then burned by heating at 1100° C. for 0.5 hour in a stream of hydrogen to produce a conventional porous metallic plate material having a thickness of 3 mm.

The overall porosity and the overall specific surface area of each of the resultant porous metallic plate materials 65 to 80 of the present invention and the conventional porous metallic plate material were measured by using an image analyzer and the BET method, respectively. The porosity of the skeleton comprising a porous sintered metal which constitutes each of the porous metallic plate materials was further measured. Table 25 show averages of the measurements obtained at 30 measurement points.

                                      TABLE 20                                     __________________________________________________________________________     COMPOSITION (Mass %)                                                               AVERAGE                                                                        PARTICLE                                                                             COMPOSITION                                                                            METAL                    WATER SOLUBLE                                                                            PLAS-                     TYPE                                                                               SIZE (μm)                                                                         (wt %)  POWDER                                                                               ORGANIC SOLVENT                                                                           SURFACTANT                                                                             RESIN BINDER                                                                             TICIZER                                                                             WATER                __________________________________________________________________________     MIXED RAW MATERIAL                                                             5a  2     Ni      65    A-(2):2    1       B-(2):2.7 --   BAL.                 5b  9     Cu      50    A-(1):0.5  2.5     B-(3):3   --   BAL.                                         A-(2):1                                                5c  20    Cu-20% Ni                                                                              70    A-(4):1    0.06    B-(6):2   --   BAL.                 5d  185   Ni      32    A-(5):2    1       B-(1):0.5 --   BAL.                     9     Cu      32                       B-(2):1                                                                        B-(4):0.6                           5e  45    Ag      75    A-(3):2    1       B-(2):1.5 --   BAL.                                         A-(2):1.5          B-(3):2                                                     A-(7):5.5                                              5f  8     SUS430  32    A-(6):0.6  4.5     B-(5):19  --   BAL.                 5g  20    Au      75    A-(8):2.5  0.5     B-(2):2   --   BAL.                 5h  0.6   W       63    A-(7):2    2       B-(1):2.5 --   BAL.                     9     Cu      4                                                                2     Ni      1                                                            __________________________________________________________________________

                                      TABLE 21                                     __________________________________________________________________________     COMPOSITION (Mass %)                                                               AVERAGE                                                                        PARTICLE                                                                              COMPOSITION                                                                            METAL ORGANIC        WATER SOLUBLE                          TYPE                                                                               SIZE (μm)                                                                          (wt %)  POWDER                                                                               SOLVENT                                                                              SURFACTANT                                                                              RESIN BINDER                                                                             PLASTICIZER                                                                            WATER                __________________________________________________________________________     MIXED RAW MATERIAL                                                             5i  2      Ni      65    A-(2):2                                                                              1        B-(2):2.7 C-(5):1 BAL.                 5j  10     Ni-15.5%                                                                               68    A-(2):1                                                                              1.5      B-(2):2   C-(1):2.5                                                                              BAL.                            Cr-8% Fe-     A-(3):0.5                                                        0.8% Mn                                                             5k  8      Co-10% Ni                                                                              52    A-(1):0.5                                                                            4.8      B-(4):2   C-(3):0.5                                                                              BAL.                 15% Cr     A-(7):2       B-(6):0.9                                                                            C-(4):1.4                                                                A-(8):6.5                C-(5):0.6                    5l  0.6    W       63    A-(7):2                                                                              1        B-(1):0.5 C-(1):0.5                                                                              BAL.                     9      Cu      4.5                  B-(2):0.5 C-(5):0.6                        3      Co      0.5                  B-(3):0.5                              5m  11     Ag-7.5% 31    A-(4):0.6                                                                            0.06     B-(5):19  C-(2):14.5                                                                             BAL.                            Cu                                                                  5n  185    Ni      32    A-(5):2                                                                              1        B-(3):2   C-(5):6.1                                                                              BAL.                     9      Cu      32                                                          5o  35     Ni-20% Cr                                                                              78    A-(2):1                                                                              0.5      B-(2):1.5 C-(4):1 BAL.                 5p  10     SUS304  60    A-(4):2.5                                                                            1.5      B-(2):2   C-(3):2 BAL.                 __________________________________________________________________________

                                      TABLE 22                                     __________________________________________________________________________               THICKNESS OR                                                         TYPE                                                                               MATERIAL                                                                             PARTICLE SIZE                                                                           SHAPE                                                       __________________________________________________________________________     REINFORCING METALLIC PLATE MATERIAL                                            A   Ni    48 mesh  WIRE CLOTH HAVING A WIRE DIAMETER OF 0.5 m                  B   Cu    0.3 mm   PARFORATED PLATE IN WHICH HOLES HAVING A DIAMETER OF 1                         mm                                                                             ARE FORMED WITH A PITCH 1.8 mm                              C   Ni    0.1 mm   PLATE MATERIAL                                              D   Au    100 mesh WIRE CLOTH HAVING A WIRE DIAMETER OF 0.1 mm                 E   SUS316L                                                                              0.3 mm   PARFORATED PLATE IN WHICH HOLES HAVING A DIAMETER OF 1                         mm                                                                             ARE FORMED WITH A PITCH 1.8 mm                              __________________________________________________________________________

                                      TABLE 23                                     __________________________________________________________________________               REINFORC-                                                                      ING                                                                  MIXED     METALLIC                                                                              PORE FORMATION CONDITION                                                                       DEGREASING CONDITION                                                                          SINTERING CONDITION                RAW   PLATE        TEMPER-        TEMPER-        TEMPER-                       MATERIAL                                                                             MATERIAL                                                                              ATMOS-                                                                               ATURE TIME                                                                               ATMOS-                                                                              ATURE TIME                                                                               ATMOS-                                                                              ATURE TIME                TYPE                                                                               SYMBOL                                                                               SYMBOL PHERE (°C.)                                                                         (min.)                                                                             PHERE                                                                               (°C.)                                                                         (m) PHERE                                                                               (°C.)                                                                         (mm)                __________________________________________________________________________     POROUS METALLIC MATERIAL OF THIS INVENTION                                     65  5a    A      AIR WITH                                                                             40    60  AIR  500   30  HYDRO-                                                                              1300  240                 66  5b    B      90% HUM-                                                                             45    40                 GEN  1030  120                 67  5c    B      IDITY 30    15       450            1150                      68  5d    A            25    30       500   60       1000  60                  69  5e    D            50    40             15  AIR  910   300                 70  5f    D            20    30       450   240 HYDRO-                                                                              1190  120                                                                 GEN                            71  5g    E            50    25       500   30  AIR  1010  60                  72  5h    E            35    120 HYDRO-                                                                              600   60  HYDRO-                                                                              1200                                                       GEN            GEN                            __________________________________________________________________________

                                      TABLE 24                                     __________________________________________________________________________               REINFORC-                                                                      ING                                                                  MIXED     METALLIC                                                                              PORE FORMATION CONDITION                                                                       DEGREASING CONDITION                                                                          SINTERING CONDITION                RAW   PLATE        TEMPER-        TEMPER-        TEMPER-                       MATERIAL                                                                             MATERIAL                                                                              ATMOS-                                                                               ATURE TIME                                                                               ATMOS-                                                                              ATURE TIME                                                                               ATMOS-                                                                              ATURE TIME                TYPE                                                                               SYMBOL                                                                               SYMBOL PHERE (°C.)                                                                         (min.)                                                                             PHERE                                                                               (°C.)                                                                         (mm)                                                                               PHERE                                                                               (°C.)                                                                         (mm)                __________________________________________________________________________     POROUS METALLIC MATERIAL OF THIS INVENTION                                     73  5i    E      AIR WITH                                                                             40    60  AIR  500   30  HYDRO-                                                                              1300  180                 74  5j    E      90% HUM-                       GEN        120                 75  5k    B      IDITY 25    15       450       VAC- 1320                                                                      UUM                            76  5l    A            50    30             15  HYDRO-                                                                              1200  30                                                                  GEN                            77  5m    E            60    60       550   120 AIR  920   120                 78  5n    E      ARGON 30    20       500   100 HYDRO-                                                                              1050                      79  5o    C      NITRO-          HYDRO-                                                                              550   120 GEN  1300  180                                  GEN             GEN                                           80  5p    C            40    60  AIR  450   30                                 __________________________________________________________________________

                  TABLE 25                                                         ______________________________________                                                   POROUS METALLIC BODY                                                                 OVERALL                                                                        SPECIFIC                                                             THICK-    SURFACE   OVERALL  POROSITY OF                                       NESS      AREA      POROSITY SKELETON                                    TYPE  (mm)      (cm.sup.2 /cm.sup.2)                                                                     (%)      (%)                                         ______________________________________                                         POROUS METALLIC PLATE MATERIAL OF THIS INVENTION                               65       2.3    390       97       22                                          66       3.2    620       95       25                                          67       6.6    410       95       31                                          68       4.0    2800      82       52                                          69       0.8    350       97       21                                          70       0.9    1150      89       41                                          71       2.1    1200      88       33                                          72       3.1    310       97       11                                          73       10.4   420       96       25                                          74       19.2   630       95       33                                          75       3.4    2400      82       52                                          76       2.4    590       92       14                                          77       5.5    660       92       22                                          78       3.3    2900      81       54                                          79       0.9    710       93       23                                          80       1.0    880       92       31                                          CONVENTIONAL POROUS METALLIC PLATE MATERIAL                                    3.0         41        95         --                                            ______________________________________                                    

The results shown in Table 25 reveal that all porous metallic bodies which constitute porous metallic plate materials 65 to 80 of the present invention have the skeleton which comprises the porous sintered metal, as shown in FIG. 1, and which has a high porosity of 10 to 60%, and that the porous metallic plates thus have extremely high specific surface areas, as compared with the conventional porous metallic plate material (Comparative Example 1) having the skeleton comprising a nonporous metal, as shown in FIG. 7.

As described above, the porous metallic plate materials of the present invention have very high specific surface areas and maintain strength due to the porous surface layers. The porous metallic plate materials thus exhibit excellent performance when applied to structural members of various machines and apparatus, and can satisfactorily comply with the demands for increasing performance and output of various machines and apparatus.

EXAMPLE 6

Description will now be made of an example in which an electrode of an alkaline secondary battery is formed.

A pure Ni powder having an average particle size of 9 μm, water-soluble methyl cellulose, glycerin, a surfactant, hexane and water were mixed in each of the compositions shown in Table 26 to form a slurry. The thus-formed slurry was formed into a sheet having a thickness of 0.4 mm by using the doctor blade method. The sheet was subjected to pore formation by being held in an atmosphere at a temperature 40° C. and humidity of 95% for the time shown in Table 26, and then dried in a far infrared dryer at a heater temperature set to 150° C. to produce a green sheet. The thus-produced green sheet was then maintained at 500° C. for 1 hour in air to remove the binder therefrom, and sintered by being held in an atmosphere of a gas mixture of H₂ --N₂ (5 to 95%) at the temperature for the time, both of which are shown in Table 26, to produce spongelike porous metallic substrates 6a to 6j having a skeleton comprising a microporous sintered metal.

The average micropore size and porosity of the skeleton of each of the spongy porous metallic substrates 6a to 6j, and the overall porosity and specific surface area of each of the spongelike porous metallic substrates 6a to 6j were measured. The results are shown in Table 26.

The average micropore size of porosity of the skeleton were measured by image analysis of a section of a sample. The overall porosity of the spongy porous metallic substrate was measured from the dimensions and weight of a sample. The overall specific surface area of the spongelike porous metallic substrate was measured by the BET method, and converted into a value per volume (a value of specific surface area per weight is obtained by the BET method).

    TABLE 26                                                                          - CHARACTERISTIC VALUE OF SUBSTANCE                                              SINTERING  AVERAGE                                                             PORE CONDITION  MICROPORE POROSITY SPECIFIC                                     SLURRY COMPOSITION (WT %) FORMATION TEMPE- HOLDING AVERAGE SIZE OF OF          SURFACE                                                                           PURE Ni METHYL  SURF-   TREATMENT RATURE TIME PORE SIZE SKELETON              SKELETON AREA                                                                    TYPE POWDER CELLULOSE GLYCERIN ACTANT HEXANE WATER (hr) (°C.)           (hr) (μm) (μm) (%) (cm.sup.2                                               /cm.sup.2)                                                                      POROUS METALLIC SUBSTRATE                                                       6a 72.7 27 5.5 10 1.9 BALANCE 2 1350 1 420 2.0 25.1 550                         6b 72.0 2.5 4.5 1.5 2.2  1 1350 3 380 0.6 12.4 400                              6c 71.5 3.0 5.0 1.2 2.5  0.5 1300 1 220 3.5 30.4 520                            6d 73.2 3.2 4.0 1.2 3.0  2 1250 1 550 7.6 28.6 460                              6e 71.0 2.5 6.0 1.0 2.5  1 1200 2 500 5.1 31.5 500                              6f 66.4 4.4 5.5 1.2 2.7  3 1150 2 620 10 33.6 690                               6g 68.5 3.0 7.0 5.0 3.0  2 1350 1 520 3.7 29.1 440                              6h 69.5 2.8 5.5 3.0 3.2  1 1120 1 660 14.8 42.0 710                             6i 73.2 2.5 5.0 2.0 1.3  2 1350 5 290 0.5 10 310                                6j 68.5 6.0 4.0 1.0 2.7  3 1100 1 690 19.3 55 1000                              CONVENTIONAL POROUS METALLIC SUBSTRATE                                          -- -- -- -- -- -- -- -- -- 460 -- -- 40                                  

A nickel (Ni) hydroxide powder having an average particle size of 10 μm, a cobalt (Co) hydroxide powder having an average particle size of 18 μm, carboxymethyl cellulose, Teflon powder and water were mixed at a ratio by weight of 100:5:0.5:4:4 to form a paste mixture. The thus-formed paste mixture was coated on the spongelike porous metallic substrates 6a to 6j shown in Table 26 so as to permeate the substrates, dried by being maintained at a temperature of 105° C. for 2 hours in atmosphere, and then press-rolled to a thickness of 0.5 mm and cut in a size of 10 cm×4 cm to produce positive electrodes (referred to as "electrodes of the present invention" hereinafter) 81 to 90 of alkaline secondary batteries of the present invention. The fill amount of nickel hydroxy powder of each of the resultant electrodes 81 to 90 of the present invention, and the average micropore size and porosity of the skeleton were measured. The results obtained are shown in Table 27.

                                      TABLE 27                                     __________________________________________________________________________         POROUS     FILLING AMOUNT                                                                           AVERAGE MICROPORE                                                                          POROSITY OF                                   METALLIC   OF Ni HYDROXIDE                                                                          SIZE OF ELECTRODE                                                                          ELECTRODE                                 TYPE                                                                               SUBSTRATE  POWDER (g)                                                                               SKELETON (μm)                                                                           SKELETON (%)                              __________________________________________________________________________     ELECTRODE OF THIS INVENTION                                                    81  6a         2.53      2.0         25.1                                      82  6b         2.53      0.6         12.4                                      83  6c         2.59      3.5         30.4                                      84  6d         2.59      7.6         28.6                                      85  6e         2.60      5.1         31.5                                      86  6f         2.61      10.3        33.6                                      87  6g         2.60      3.7         29.1                                      88  6h         2.60      14.8        42.0                                      89  6i         2.51      0.5         10.0                                      90  6j         2.59      19.3        55.0                                      CONVENTIONAL ELECTRODE (COMPARATIVE EXAMPLE 2)                                 CONVENTIONAL   2.55      --          --                                        POROUS METALLIC                                                                SUBSTRATE                                                                      __________________________________________________________________________

Each of these electrodes 81 to 90 of the present invention and a conventional electrode was used as a positive electrode, and a terminal is spot-welded at a predetermined position of the electrode. The electrode was then wound through a known cadmium negative electrode and a separator, and sealed in a can together with an electrolyte of a 35% potassium hydroxide aqueous solution to produce a Size AA nickel-cadmium secondary battery.

All of the thus-obtained nickel cadmium secondary batteries were initialized by repeating charging and discharging operations 5 times under conditions in which the charging time is 10 hours and the discharging time is 2 hours, and then subjected to a life test by repeating complete charging and discharging operations 2,000 times under conditions in which the charging time is 5 hours and the discharging time is 2 hours. In this life test, the discharge capacity of each of the batteries was measured at the first and after 2,000 operations, and the results obtained are shown in Table 28. When the discharge capacity became below 80% of the first discharge capacity before the number of operations did not reach 2,000 times, the time the discharge capacity became under 80% of the first discharge capacity was regarded as the life of the battery, and the life test was stopped. The number of times of operations for each battery is shown in Table 28. After the life test, the battery was dismantled, and the degree of electrolyte impregnation of the separator was measured. These results obtained are shown in Table 28.

                                      TABLE 28                                     __________________________________________________________________________                                                    DEGREE OF ELECTROLYTE                                LIFE OF NICKEL-CADIUM SECONDARY BATTERY                                                                  IMPREGNATION OF                      ELECTRODE       1st DISCHARGE                                                                           2000th DISCHARGE                                                                          NUMBER                                                                               SEPARATOR AFTER TEST            TYPE SHOWN IN TABLE 2                                                                               CAPACITY (mAh)                                                                          CAPACITY (mAh)                                                                            OF TIMES                                                                             (vol. %)                        __________________________________________________________________________     ICKEL-CADIUM SECONDARY BATTERY                                                 81   ELECTRODE OF  1 711      621        2000 MORE                                                                            86.5                            82   THIS INVENTION                                                                               2 706      583        2000 MORE                                                                            72.9                            83                 3 742      622        2000 MORE                                                                            88.3                            84                 4 730      614        2000 MORE                                                                            86.1                            85                 5 737      598        2000 MORE                                                                            87.2                            86                 6 746      615        2000 MORE                                                                            84.7                            87                 7 739      605        2000 MORE                                                                            73.7                            88                 8 741      601        2000 MORE                                                                            78.6                            89                 9 702      579        2000 MORE                                                                            71.2                            90                 10                                                                               737      603        2000 MORE                                                                            75.9                            91   CONVENTIONAL ELECTRODE                                                                         720      --          958  40.5                                 (CONVENTIONAL EXAMPLE 2)                                                  __________________________________________________________________________

Comparative Example 2

For comparison, Ni was deposited to a thickness of 20 μm on a urethane foam having an average pore size of 500 μm by electroless plating, and then held in air at 500° C. for 0.5 hour. The urethane component was then burned by holding the urethane foam in an atmosphere of a gas mixture containing H₂ --N₂ (5 to 95%) at 950° C. for 1 hour to produce a conventional porous metallic substrate. The overall porosity and specific surface area of the resultant conventional porous metallic substrate are shown in Table 26.

A conventional positive electrode (referred to as a "conventional electrode" hereinafter) of an alkaline secondary battery was produced by the same method as Example 6 except that the conventional porous metallic substrate shown in Table 26 was used, and the fill amount of the Ni hydroxide powder was measured.

FIG. 8 shows the sectional structure of the electrode in accordance with this comparative example. As shown in FIG. 8, in a spongelike porous metallic substrate having pores 1 formed by three-dimensional continuous network connection of a skeleton 2 comprising Ni metal, the pores are filled with an active material.

The conventional electrodes was subjected to the same life test as Example 6. The results obtained are shown in Table 28.

COMPARISON BETWEEN EXAMPLE 6 AND COMPARATIVE EXAMPLE 2

The results shown in Table 28 reveal that nickel-cadmium secondary batteries 81 to 90 respectively comprising the electrodes 80 to 90 of the present invention show larger number of times of operation and longer lives than nickel-cadmium secondary battery 91 (Comparative Example 2).

Although, in the example of the present invention, the electrodes 81 to 90 of the present invention are assembled into nickel-cadmium secondary batteries for the life test, the electrodes 81 to 90 of the present invention respectively comprising the spongelike porous metallic substrates 6a to 6j shown in Table 27 may be assembled into nickel-hydrogen batteries for the life test. In this case, the lives of the secondary batteries were increased. It was further found that even when the spongelike porous metallic substrates 6a to 6j shown in Table 26 are used as negative electrodes of nickel-cadmium secondary batteries or nickel-hydrogen secondary batteries, increases in lives can be attained.

As described above, the use of the electrode of an alkaline secondary battery of the present invention exhibits the following excellent effects:

(1) Since the electrolyte held in the micropores of the skeleton comprising a microporous sintered metal oozes out when the electrolyte in the alkaline secondary battery is consumed, this supplements the shortage of electrolyte, thereby increasing the life of the battery.

(2) When the electrolyte is solidified by corrosion of a can and thus becomes insufficient, the electrolyte held in micropores of the skeleton of the spongelike porous metallic substrate used as a negative electrode which contacts the can of a closed alkaline secondary battery oozes out, supplementing the shortage of electrolyte, thereby increasing the life of the battery.

(3) When the meso-pores formed in surfaces of a positive active material powder are increased and start swelling, the electrolyte oozes out from the microporous skeleton of the spongelike porous metallic substrate used for a positive electrode in an amount corresponding to the amount of the electrolyte used for swelling, preventing exhaustion of the electrolyte, and thereby increasing the life of the battery.

EXAMPLE 7

Description will now be made of another example in which an electrode of an alkaline secondary battery is formed.

Each of the spongelike porous metallic substrates 6a to 6j shown in Table 26 was dipped in a saturated nickel nitrate aqueous solution at a temperature of 25° C. for 10 minutes, taken out of the solution, and then dried by being held in a dryer at a temperature of 110° C. for 10 minutes. The substrate was then dipped in a 25% potassium hydroxide aqueous solution at 50° C. for 10 minutes, taken out of the solution and then dried by being held in a dryer at a temperature of 110° C. for 30 minutes to convert into nickel hydroxide and fill the pores of each of the spongelike porous metallic substrates 6a to 6j and the micropores of the skeleton with nickel hydroxide.

Although the micropores of the skeleton of each of the spongelike porous metallic substrates 6a to 6j which were treated as described above were filled with nickel hydroxide, nickel hydroxide films were merely formed on the inner walls of the large pores of each of the spongelike porous metallic substrates 6a to 6j, and the large pores were not sufficiently filled with nickel hydroxide. Therefore, the pores were filled with nickel hydroxide by the treatment below to produce positive electrodes (referred to as "electrodes of the present invention" hereinafter) 92 to 101 of alkaline secondary batteries of the present invention.

Namely, the surface of each of the spongelike porous metallic substrates 6a to 6j treated as described above was coated with a paste mixture comprising a Ni hydroxide powder having an average particle size of 10 μm, a Co hydroxide powder having an average particle size of 18 μm, carboxymethyl cellulose, Teflon powder and water at a ratio by weight of 100:5:0.5:4:41 so that the substrate was impregnated with the mixture. The substrates were dried by being held in air at a temperature of 105° C. for 2 hours, rolled under pressure to a thickness of 0.5 mm and then cut in a size of 10 cm×4 cm to produce electrodes 92 to 101 of the present invention.

The amount of the Ni hydroxide powder contained in each of thus-obtained electrodes 92 to 101 of the present invention was measured. The results obtained are shown in Table 29. For comparison, a conventional positive electrode (referred to as a "conventional electrode" hereinafter) of an alkaline secondary battery was produced by the same method as described above except that the conventional nickel foam shown in Table 26 was used, and the amount of Ni hydroxide powder contained in the conventional electrode was measured. The result is shown in Table 29.

Each of invention electrodes 92 to 101 of the present invention was used as a positive electrode, and a terminal was spot-welded at a predetermined position of the electrode. The positive electrode was then wound through a known cadmium negative electrode and a separator, and sealed in a can together with a 35% potassium hydroxide aqueous solution to produce a Size AA nickel-cadmium secondary battery.

Each of all resultant nickel-cadmium secondary batteries was first initialized by repeating charging and discharging operations 5 times under,conditions in which the charging time is 10 hours, and the discharging time is 2 hours, and then repeatedly completely charged and discharged 500 times under conditions in which the charging time is 5 hours and the discharging time is 2 hours. The discharge capacity was measured at the 1st, 250th and 500th operations, and the results obtained are shown in Table 29.

The results shown in Table 29 reveal that the electrodes 92 to 101 of the present invention contain. larger amounts of Ni hydroxide than the conventional electrode, and that the nickel-cadmium secondary batteries respectively comprising the electrodes 92 to 101 of the present invention have higher capacity than the nickel-cadmium secondary battery comprising the conventional electrode.

Although, in this example of the present invention, the electrodes 92 to 101 of the present invention were assembled into the nickel-cadmium secondary batteries for the capacity test, the electrodes 92 to 101 of the present invention respectively comprising the spongelike porous metallic substrates 6a to 6j shown in Table 29 may be assembled into nickel-hydrogen secondary batteries so that the capacities are increased. It was also found that an increase in capacity can be achieved by filling the spongelike porous metallic substrates 6a to 6j shown in Table 29 with an active material other than nickel hydroxide.

As described above, the use of the electrode of an alkaline secondary battery of the present invention exhibits the excellent effects of increasing the amount the active material contained in the electrode, and promoting an increase in capacity of the battery.

                                      TABLE 29                                     __________________________________________________________________________                                      CAPACITY OF NICKEL-CADIUM SECONDARY                                            BATTERY                                           POROUS METALLIC                                                                             CONTENT OF Ni HYDROXIDE                                                                        1st DISCHARGE                                                                           250th DISCHARGE                                                                           500th DISCHARGE           TYPE                                                                               SUBSTRATE USED                                                                              OF ELECTRODE (g)                                                                               CAPACITY (mAh)                                                                          CAPACITY (mAh)                                                                            CAPACITY                  __________________________________________________________________________                                                          (mAh)                     ELECTRODE OF THIS INVENTION                                                    92  6a           3.02            866      798        779                       93  6b           3.00            860      805        771                       94  6c           3.11            890      836        788                       95  6d           3.05            876      825        782                       96  6e           3.00            860      808        765                       97  6f           3.09            885      835        780                       98  6g           3.11            888      810        779                       99  6h           3.35            959      898        850                       100 6i           3.04            870      821        779                       101 6j           3.20            912      860        815                       CONVENTIONAL ELECTRODE                                                         CONVENTIONAL POROUS                                                                             2.25            720      658        623                       METALLIC SUBSTRATE                                                             __________________________________________________________________________ 

What is claimed is:
 1. A porous metallic material with a high specific surface area comprising a skeleton in a three-dimensional network structure which is composed entirely of a sintered metal powder having a porosity of 10 to 60%, wherein the overall porosity is 80 to 99%.
 2. A porous metallic material with a high specific surface area according to claim 1, wherein the overall specific surface area is 300 to 11000 cm² /cm³.
 3. A porous metallic material according to claim 1, wherein the pores formed by the skeleton have an average pore size of 60 to 700 μm.
 4. A porous metallic plate material with a high specific surface area comprising a skeleton in a three-dimensional network structure which is composed entirely of a sintered metal powder having a porosity of 10 to 60%, and a porous surface layer which is provided on one or both sides of the metallic plate material and which has pores formed by the skeleton which are relatively smaller than internal pores, wherein the overall porosity is 80 to 99%.
 5. A porous metallic plate material with a high specific surface area comprising a porous metallic body and a reinforcing plate, wherein the porous metallic body comprises a skeleton in a three-dimensional network structure which is composed entirely of a sintered metal powder having a porosity of 10 to 60%, and the overall porosity is 80 to 99%.
 6. A porous metallic plate material according to claim 5, wherein the reinforcing plate is selected from a network material, a plate and a perforated plate.
 7. A porous metallic plate material according to claim 5 or 6, wherein the reinforcing plate is held in the porous metallic body.
 8. A method of producing a porous metallic material according to claim 1, comprising the steps of:preparing a foamable slurry containing a metal powder; forming the foamable slurry; drying the formed product; and burning the dry formed product.
 9. A method of producing a porous metallic material according to claim 8, wherein the foamable slurry contains a foaming agent, a water-soluble resin binder and a surfactant.
 10. A method of producing a porous metallic material according to claim 8, further comprising the foaming step between the forming step and the drying step.
 11. A method of producing a porous metallic material according to claim 8, the metal powder has an average particle size of 0.5 to 500 μm. 